1H NMR study of thermo-induced collapse of polyelectrolyte microgels

Abstract

Smart polymer gels of microscale size are attracting a lot of attention since their properties, such as fast response to various external stimuli, make them suitable candidates for many potential applications including drug delivery, nanoreactors, or separation techniques. In this research, thermosensitive microgels of poly(N-isopropylacrylamide), poly(N-vinylcaprolactam), poly(N-isopropylacrylamide-co-sodium vinylsulfonate) and poly(N-vinylcaprolactam-co-1-vinylimidazole) were prepared via aqueous free-radical precipitation polymerization. The thermo-induced collapse of the microgels and subchain mobility were thoroughly investigated by means of proton nuclear magnetic resonance (1 H NMR) spectroscopy, as well as scanning electron microscopy and dynamic light scattering. It was found that in copolymer microgels a part of the thermosensitive monomer units does not collapse upon heating, and the critical temperature is not affected strongly by the addition of ionogenic groups. That could be explained by non-uniform monomer unit distribution, leading to the appearance of thermosensitive core-charged corona structure of the microgel particle. Сore-corona architecture of microgels results in film formation with the ordering of the self-assembly structure.

Towards the realistic computer model of precipitation polymerization microgels

“…Thermosensitive microgels were synthesized by free-radical thermo-initiated precipitation polymerization in water in the presence of BIS cross-linker (NIPA concentration in water - 0.01 g/ml, BIS - 1 molar percent to NIPA, PS - 3 molar percent to NIPA). Detailed description of the synthetic procedure could be found in our experimental paper 38 .…”